Drive mechanism

ABSTRACT

A reciprocable member provided with a continuous gear track is driven over a rectilinear path of travel by a single reciprocable drive gear which is in mesh with the gear track or a pair of drive gears on opposite sides of the track. The driven member is restrained by guide means for movement along a rectilinear path, and the drive gear is rotatable to effect the reciprocation of the driven member. A load-supporting frame is positioned adjacent the reciprocable driven member and supports a pair of rotatable sheaves over which a flexible element is trained with one end of the flexible element being joined to the driven member. A load can thus be attached to the other end of the flexible element with its weight being carried by the aforementioned support frame.

United States Patent Dobbs [451 Aug. '22, 197 2 [541 DRIVE MECHANISM [72] Inventor: Richard H. Dobbs, Winfield, Kans.

[73] Assignee: Harriette E. Dobbs, Winfield, Kans.

[22] Filed: Aug. 31, 1970 [21] Appl. No.: 68,331

[52] US. Cl ..74/31 [51] Int. Cl ..Fl6h 19/04 [58] Field of Search ..74/31 [56] References Cited UNITED STATES PATENTS I 1,848,992 3/l932 Bullock .......74/3l 2,208,590 7/ 1940 Leonard et al. ..74/3l 2,732,722 l/l956 Welshusen ..74/31 Primary Examiner-William F. ODea Assistant Examiner-Wesley S. Ratliff, Jr. Attorney-Schmidt, Johnson, Hovey & Williams ABSTRACT A reciprocable member provided with a continuous gear track is driven over a rectilinear path of travel by a single reciprocable drive gear which is in mesh with the gear track or a pair of drive gears on opposite sides of the track. The driven member is restrained by guide means for movement along a rectilinear path, and the drive gear is rotatable to effect the reciprocation of the driven member. A load-supporting frame is positioned adjacent the reciprocable driven member and supports a pair of rotatable sheaves over which a flexible element is trained with one end of the flexible element being joined to the driven member. A load can thus be attached to the other end of the flexible element with its weight being carried by the aforementioned support frame.

6 Claims, 17 Drawing Figures jail- "iii. l lllllllllllllllllllllllllmmmllllll lllmi g fllllllflllifl lli'l I, /za /z/ m 7 1i, W221 426' l in l ll I /2/ L 255 #5 i1 l9? w I gill PATENTEDAUGZZ I972 SHEET 1 IF 4 INVEAI'TOR Richard H. Dobbs 133/ g 2L 2 gig 7 4 ATTORNEYS PATENTEDauszz m2 SHEEI 3 0F 4 A TTORNE V5,

DRIVE MECHANISM This invention relates to a drive mechanism for moving a load over a reciprocating path of travel.

In apparatus such as oil well pumps and the like, it is necessary to move a relatively large load over a reciprocating path of travel. Drive mechanisms for such apparatus have previously been limited to structure for effecting movement of a driven member in a nonlinear manner. Such nonlinear travel of the drive mechanism results in a loss of efficiency and also places added strain on the drive mechanism because of the torsional forces produced.

It is, therefore, the primary object of the present invention to provide drive mechanism which is operable upon simultaneous rotation and reciprocation of a drive gear to move a driven member over a rectilinear path of travel and thus increase the efficiency of the drive mechanism.

Another object of the invention is to limit movement of the drive gear along a rectilinear path of travel thereby avoiding any torsional forces between the drive gear and the driven member.

A still further object of the invention is to provide a reciprocable drive mechanism which can be coupled with a flexible element trained over a load-supporting member to move a load secured to the flexible element and carried by the load-supporting member.

Referring to the drawings:

FIG. 1 is a front elevational view of one form of the invention with portions being broken away to illustrate the manner in which the drive gear is reciprocated;

FIG. 2 is a partial side elevational view of the apparatus shown in FIG. 1 with portions of the framework being broken away for purposes of illustration,

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. I and with portions being broken away to illustrate the relationship of the guides with their corresponding tracks;

FIG. 4 is a schematic illustration of the apparatus of FIGS. 1-3 illustrating the relationship of the component parts after the driven member and the drive gear have moved relatively;

FIG. 5 is a partial front elevational view of an alternative form of the invention;

FIG. 6 is a cross-sectional view taken along line 66 of FIG. 5;

FIG. 7 is a front elevational view of another modified form of the invention with portions being broken away for purposes of illustration;

FIG. 8 is an enlarged, cross-sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is a side elevational view of the apparatus shown in FIG. 7, again with portions being broken away for clarity;

FIG. 10 is a front elevational view of a modified form of driven element which can be utilized in the invention;

FIG. 11 is a front elevational view of yet another alternative form of the drive mechanism with portions of the supporting framework being broken away for purposes of illustration;

FIG. 12 is a side elevational view of the apparatus shown in FIG. 11 with portions of the framework again being broken away for purposes of illustration;

FIG. 13 is a cross-sectional view of the apparatus shown in FIGS. 11 and 12 taken along line 1313 of FIG. 1 1;

FIG. 14 is a side elevational view of the drive sheave 7 shown in cross section in FIG. 11;

FIG. 15 is a front elevational view of still another form of the invention with portions being broken away to illustrate details of construction;

FIG. 16 is a side elevational view of the apparatus shown in FIG. 15 with portions being broken away for clarity; and

FIG. 17 is a cross-sectional view taken along line 17-17 ofFlG. 15.

Referring initially to the embodiment of the invention illustrated in FIGS. 14, a reciprocable driven member 20 is restrained for movement along a rectilinear path of travel by an upright guide frame 22 which is supported upon a base 24. The driven member 20 comprises a rectangular plate 26 which includes a generally elliptical, internally toothed portion that presents a gear track 28. The rectangular plate 26 also includes a first pair of projections 30 visible in FIG.- 1,

each of which comprises a pair of spaced, parallel stretches joined at the ends by interconnecting portions to present a surface in the form of a continuous track. A second pair of projections 32, which are identical to the projections 30, are disposed on the side of the plate 26 opposite the projections 30 and are partially visible in FIG. 3. I

A reciprocable drive gear 34 is in mesh with the gear track 28 and is rigid with a drive shaft 36 which extends through the drive gear and projects'therefrom in opposite directions. A pair of spacers 38 (FIG. 3) on the drive shaft maintain the gear 34 in proper relationship to the gear track 28. A first support extension 40 (FIG. 1) is secured to one side of the guide frame 22 by welding or other appropriate means, and a second support extension 40 (FIG. 3) is disposed on the opposite side of the frame 22. Each of the extensions 40 has spaced, parallel, upper arms 42 (FIG. 3) and a similar pair of spaced lower arms 44, one of which is visible in FIG. 1.

The arms 42 and 44 of each of the extensions 40 are rigid with a central bight portion 46. The vertically disposed planar surfaces of the arms 42 and 44 support a pair of elongated, linear passage-defining frame ele-' ments 48 (FIG. 2) which are transversely disposed ad- 45 jacent opposite sides of the driven member 20 and secured to the arms 42 and 44 by welding or other appropriate means. Each of the frame elements 48 supports an elongated, rectangular body 50 of smaller dimensions than the internal dimensions of the corresponding frame element to permit movement of thebodies 50 within the passages presented by-elements 48.

The drive shaft 36 is joumaled in each of the bodies 50 to support the latter within their respective frame elements for reciprocating movement with the drive gear 34. Each of the bodies 50 is provided with a pair of spaced roller guides 52 which project from the bodies 50 through appropriate slots 54 in the corresponding frame elements 48 to engage the surfaces of the corresponding tracks presented by the projections 30.

As is evident from viewing FIG. 2, the drive shaft 36 projects outwardly from one of the frame elements 48 and is provided with a sheave 56 which is rotatable by a drive belt 58. An appropriate power source 60 which may be a conventional electric motor, is positioned on the base 24 and rotates a drive sheave 62 through a belt 64, the sheave 62, in tum, driving the belt 58 which passes therearound. As the drive shaft 36 is rotated to thereby rotate the drive gear 34, the shaft 36 is free to reciprocate relative to the frame elements 48 by virtue of the slots 54 for roller guides 52 and a third slot 65 in the vertical wall of the frame element 48, which slot is visible in FIG. 1.

A pair of eyelets 66 are rigid with the plate 26 at the uppermost leading edge thereof and provide means for securing a pair of flexible elements such as cables 68 to the driven member 20 for supporting a load in a manner which will be fully explained in the subsequent description of a modified form of the invention.

In operation, when the power source 60 is energized and the drive shaft 36 rotated, assuming the rotation of the shaft 36 and hence the drive gear 34 is counterclockwise when viewing FIG. I, the drive gear 34 moves in mesh with the gear track 28 to the right until it is in engagement with the right-hand stretch of the generally elliptical gear track. As this movement oc curs, the guide rollers 52 simultaneously move to a position engaging the right-hand stretches of their corresponding tracks as shown in the schematic illustration of FIG. 4. As the gear 34 continues to rotate in a counterclockwise direction the driven member 20 moves upwardly relative to the drive gear and the frame elements 48 until the lower portion of the gear track 28 is in mesh with the drive gear 34. When this latter position is reached with the drive gear 34 continuing to rotate in a counterclockwise direction, the gear moves back to the left around the curved portion of the track 28 and into mesh with the left-hand stretch of the gear track. During this movement the rollers 52. are in continuous engagement with their respective tracks. Further counterclockwise rotation of the drive gear 34 returns the driven member 20 to the position illustrated in FIG 1.

The fact that the guide rollers 52 are in continuous engagement with the surfaces of their corresponding tracks serves two important functions. First of all, they facilitate guiding of the member 20 along a rectilinear path of travel while also helping to assure that the reciprocating movement of the member is frictionless and does not bind within the frame 22. Secondly, the rollers 52 guide the rectangular bodies 50 and hence the drive shaft 36 in a rectilinear path of travel within the frame elements 48 while assuring relatively frictionless movement of these bodies and preventing binding forces from acting upon them as they reciprocate within the frame elements.

In the alternative form of the invention illustrated in FIGS. and 6, a reciprocable driven member 120 comprises a generally rectangular plate 126 having a generally elliptical externally toothed portion 70 which presents a continuous gear track 128. The driven member 120 is reciprocated over a rectilinear path of travel within the confines of the guide frame 22 by a rotatable drive gear 134 which is rigid with a drive shaft 136. The gear 134 is held in mesh with the gear track 128 by first and second guide components 82 which continuously engage a guide panel 72 that circumscribes the gear track 128 in spaced relationship thereto. A single elongated, linear frame element 148 of tubular configuration is disposed transversely of the driven member 120 and secured to the guide frame 22 by welding or other appropriate means. An elongated,

generally rectangular solid body 150 is disposed within the frame element 148, and a pair of roller guides 152 project from the body 150 and extend through an appropriate slot l54 in the frame element 148 as illustrated in FIG. 6. A second slot 165 is provided for the drive shaft 136 which is joumaled in the body 150 and projects outwardly from the frame element 148. Although not shown in FIGS. 5 and 6, it is to be understood that a sheave such as the sheave 56 illustrated in FIG. 2 would normally be provided on the outwardly extending end of the shaft 136 and this sheave would be coupled with a power source in a manner similar to that illustrated for the embodiment of FIGS. l-4.

Operation of the alternative embodiment of FIGS. 5 and 6 is similar to that previously described for the embodiment of FIGS. 1-4. As the drive gear 134 is rotated it is guided over a rectilinear path of travel by the body 150 and the frame element 148, and the driven member 120 is simultaneously guided over a rectilinear path of travel by the guide frame 22. The guide panel 72 presents a pair of spaced surfaces parallel with the path of travel of the driven member 120 and the spaced guide rollers 152 alternately engage the respective surfaces as the body 150 is shifted from one end of its path of reciprocation to the other.

Referring now to FIGS. 7-9 wherein another alternative embodiment of the invention is illustrated, it is seen that the guide frame 22 has a pair of upright support staffs 74 positioned adjacent thereto and extending upwardly from the base 24 to support a pair of sheaves 76 joumaled on a shaft 78. A driven member 220 which is similar to the member 120 previously described, comprises a generally rectangular plate 226 having a generally elliptical, externally toothed portion 170 which presents a continuous gear track 228. First,

second, third and fourth rollers are mounted at each of the corners of the plate 226 in the manner illustrated in FIG. 9.

A drive gear 234 is secured to a drive shaft 236 and held in mesh with the gear track 228 by virtue of first and second roller components 82, mounted on shaft 235, which are in continuous engagement with a guide panel 172 that circumscribes the gear track 228 in spaced relationship thereto. The drive shaft 236 is journaled in an arm 84 which connects the shaft 236 with a second shaft 86. A first sprocket 88 is rigid with the shaft 236, and a second sprocket 90 is rigid with the shaft 86. A drive chain 92 interconnects the sprockets 88 and 90 for simultaneous rotation, and a drive sheave 94 rigid with the shaft 86 drives the sprockets 88 and 90 and hence the gear 234 through belt 164 coupled with an appropriate power source such as an electric motor 60.

A pair of pegs 96, one of which is visible in FIG. 7, provide means for connecting one of the ends of a pair of flexible elements such as cables 68 to the driven member 120. The cables 68 are trained over the sheaves 76 on the support staffs 74 and the other ends of the cables 68 are secured to a pitman rod 98 by a yoke plate 100.

Operation of the embodiment of FIGS. 7-9 is similar to that previously described for the embodiments of FIGS. 1-4 and 5-6, although the reciprocation of the drive gear 234 is guided by the connecting arm 84 as the sprockets 88 and 90 effect rotation of the drive gear. Furthermore, the provision of rollers 80 reduce friction between the driven member 120 and the guide frame 22 as the member reciprocates over its rectilinear path of travel relative to the guide frame. It will be appreciated that the arrangement of the support staffs 74 and the sheaves 76 relative to the guide frame 22 is applicable to each of the embodiments previously described and this arrangement is, in fact, intended to be indicated by the presence of the cables 68 in both of the embodiments of FIGS. 1-4 and 5-6.

FIG. illustrates a modification of the embodiment of FIGS. 7-9 by the provision of a driven member 220' having a generally elliptical, internally toothed portion which presents a continuous gear track 228' similar to that illustrated in the embodiment shown in FIG. 1, and also including a centrally disposed guide panel projection 172 which presents a surface in spaced relationship to the gear track 228 for the roller components 82 (not shown in FIG. 10) to engage for maintaining the drive gear 234 in mesh with the gear track. Operation of this modified form of the invention is identical to that previously described for the embodiment of FIGS. 7-9.

A still further alternative form of the invention is il- Iustrated in FIGS. 11-14. A reciprocable driven member 320 is restrained for movement along a rectilinear path of travel by an upright guide frame 122 which is supported upon a base 124. The driven member 320 comprises a generally rectangular plate 326 which includes a circular, externally toothed portion 270 that presents a continuous gear track 328. A pair of upright support staffs 174 are disposed adjacent the guide frame 122 and extend upwardly from the base 124 to support a pair of sheaves 176 which are journaled on a shaft 178. Yieldable means such as cables 168 are trained over the sheaves 176 with one end of the cables being secured to the plate 326 through fastenings pegs 196. The other ends of the cables 168 are secured to a pitman rod 98 through a yoke plate 100 as previously described for the embodiment of FIGS. 7-9.

A drive gear 334 (FIG. 12) is mounted upon a shaft 336, the latter also mounting a bevel gear 102 and a pair of roller components 182 disposed on opposite sides of the drive gear 334. The drive gear 334 is held in mesh with the gear track 328 by virtue of the roller components 182 engaging the surface of a guide panel 372 which is spaced from and circumscribes the gear track 328.

An elongated, linear, passage-defining frame element 248 is transversely disposed adjacent the driven member 320 and is secured to the guide frame 122 by welding or other appropriate means. A hollow body 250 supports the drive shaft 336 and also mounts a second shaft 104 of a second bevel gear 106. The hollow interior of the body 250 permits rotation of the bevel gear 102 therewithin as is apparent from FIG. 13. An extension of the shaft 104 defines a socket 108 which receives a drive shaft 110 rigid with a drive sheave 112. The sheave 112, is in turn, coupled with an appropriate power source such as an electric motor 60 through a drive belt 1 14.

Operation of the alternative embodiment of FIGS. ll-l4 is similar to that discussed above for the previ- 112 rotates the bevel gear 106 which, in turn, drives the shaft 336 through the bevel gear 102. As the drive gear 334 rotates with the shaft 336, the driven member 320 reciprocates over a vertical rectilinear path of travel while the drive gear 334 simultaneously reciprocates over a horizontal rectilinear path of travel at 90 to the path of travel of the driven member 320.

Another alternative form of the invention is illustrated in FIGS. 15-17. A reciprocable driven member 420 is restrained for movement along a rectilinear path of travel by an upright guide frame 222 which is supported upon a base 224. The driven member 420 comprises a generally rectangular plate 426 having rollers 180 disposed at each of its four corners to facilitate movement relative to the frame 222. A generally elliptical, externally toothed portion 370 presents a continuous gear track 428. A guide panel 472 circumscribes the gear track 428 in spaced, parallel relation thereto for purposes to be made clear hereinafter.

An elongated, linear frame element 348 is mounted transversely of the frame 222 by a plurality of brackets 116. The frame element 348 provides a housing for a drive mechanism which includes a first drive gear 434 disposed for continuous engagement with the gear track 428, and second and third drive gears 434 spaced on either side of the firstmentioned drive gear with one or the other of the latter two mentioned gears being in engagement with the gear track 428 at any given time. Each of the gears 434 is mounted upon a shaft 436 and each shaft extends through a pair of spaced carrier plates 118 with a spur gear 121 being mounted on each of the shafts 436 intermediate the plates 118 in intermeshed relationship to an adjacent spur gear 121. Spacers 123 on each of the shafts 436 maintain the spur gears 121 in proper relationship. It is to be noted that the shaft 436 of the centrally disposed drive gear 434 is somewhat longer than the shafts 436 of the other two drive gears for the purpose of mounting a roller component 282.

A shaft 125 is journaled through one of the plates 118 for mounting a gear 127 in mesh with one of the spur gears 121. The shaft 125 is keyed to a first sprocket 188 which is coupled with a second sprocket 190 through a drive chain 192. An electric motor turns a belt 264 which, in turn, rotates a sheave 194 keyed to the sprocket 190.

A pair of flexible cables 268 are secured to the driven member 420 at the uppermost end of the latter and are trained over a pair of sheaves 276 as previously ously described embodiments. Rotation of the sheave described for the embodiments of FIGS. 7-9 and 1l-l4. The sheaves 276 are rotatably mounted upon a shaft 278 which is supported by upright support staffs 274. The cables 268 are then secured to a pitmanrod 98 through a yoke plate as previously described for the embodiment of FIGS. 7-9.

Operation of the embodiment of FIGS. 15-17 is similar to that described for the embodiment of FIGS. 11-14. Assuming that the motor 60 effects rotation of the drive shaft and hence the gear 127 in a clockwise direction when viewing FIG. 15, the centrally disposed spur gear 121 and its associated drive gear 134 are also rotated in a clockwise direction, while the other two spur gears 121 and their associated drive gears 434 are rotated in a counterclockwise direction. Thus, the two drive gears 434 which are shown in engagement with the gear track 428 in FIG. 17 cause the driven member 420 to move upwardly relative .to the frame 222. When the member 420 reaches the upper limit of its reciprocating path of travel, the gears 434 are at the lower end of the gear track 428. Continued rotation of the gears 434 causes the same to shift to the left, when viewing FIG. 17, until the centrally disposed gear 434 is in engagement with the left-hand side of the gear track 428, and the gear 434 which is meshed with the gear 127 is in engagement with the right-hand stretch of the gear track 428. Appropriately spaced openings in the guide panel 472 permit this transverse reciprocation of the drive gears 434. Continued rotation of the drive gears 434 effects reciprocation of the driven member 420 in the opposite direction until it reaches the lowermost limit of its path of travel where the drive gears 434 shift back to the position illustrated in FIG. 17.

It will be appreciated that, by virtue of the parallel drive gears 434 in the above described embodiment, a highly efficient reciprocating drive mechanism is ob tained. Since two of the drive gears 434 are always in engagement with the gear track 428, the drive force on the member 420 is equalized and any tendency for the member 420 to bind relative to the frame 222 is eliminated.

While the drive mechanism of the invention has been found particularly useful in oil well applications where heavy loads are exerted on the mechanism, it will be appreciated that advantages are to be obtained in utilizing the invention in any instance where it is desirable to eliminate torsional forces on the drive gears and confine the movement of a driven member to a precise rectilinear path of travel.

Having thus described the invention, what is claimed as new and described to be secured by Letters Patent is:

1. Drive mechanism comprising:

a reciprocable driven member having a continuous gear track;

guide means restraining said member for movement along a rectilinear path of travel;

a reciprocable drive gear in mesh with said gear track,

said drive gear being rotatable to effect reciprocation of said driven member as the drive gear is reciprocated;

second and third rotatable, reciprocable drive gears spaced on opposite sides of the first-mentioned gear; and

means operably coupling each of said second and third gears with the first-mentioned gear for rotation and reciprocation therewith whereby one of said second and third gears meshes with said gear track during reciprocation of said gears in one direction and the other of said second and third gears meshes with said gear track during reciprocation of said gears in the opposite direction.

2. Drive mechanism as set forth in claim 1, wherein each of said gears is provided with a shaft rigid therewith and projecting therefrom and said gear coupling means comprises first, second, and third intermeshed spur gears mounted on the respective gear shafts.

3. Drive mechanism as set forth in claim 2, including a power-driven gear in mesh with one of said second and tBird spur ears for rotating the same.

. rive mec anism compris ng:

a reciprocable driven member having a continuous gear track;

guide means restraining said member for movement along a rectilinear path of travel;

a reciprocable drive gear in mesh with said gear track,

said drive gear being rotatable to effect reciprocation of said driven member as the drive gear is reciprocated;

a drive shaft for effecting rotation of said drive gear;

an elongated linear frame element transversely disposed adjacent said member;

a body disposed within said element,

said drive shaft being journaled in said body and supported by the latter whereby said frame element guides said body and thus said drive gear along a rectilinear path of reciprocation;

means projecting from said member and presenting a pair of spaced surfaces parallel with said path of travel; and

first and second spaced guides supported by said body and projecting therefrom whereby as said body reciprocates with said drive gear said guides alternately engage the respective surfaces as said member reciprocates,

each of said surfaces comprising a pair of spaced,

parallel stretches joined at the ends by interconnecting portions to define a continuous track and each of said guides is disposed for continuous engagement with a corresponding track.

5. Drive mechanism as set forth in claim 4, wherein said member includes a generally elliptical internally toothed portion presenting said gear track.

6. Drive mechanism as set forth in claim 4, including a second elongated linear frame element transversely disposed adjacent said member on the side opposite the firstmentioned frame element; a second body supported by said second frame element, said drive shaft being journaled in said second body; means projecting from said member and presenting a second pair of spaced surfaces on the side of said member opposite the first-mentioned surfaces and parallel with said path of travel; and second and third guides supported by said second body and projecting therefrom for continuous engagement with acorresponding track as said second body reciprocates with said drive gear. 

1. Drive mechanism comprising: a reciprocable driven member having a continuous gear track; guide means restraining said member for movement along a rectilinear path of travel; a reciprocable drive gear in mesh with said gear track, said drive gear being rotatable to effect reciprocation of said driven member as the drive gear is reciprocated; second and third rotatable, reciprocable drive gears spaced on opposite sides of the first-mentioned gear; and means operably coupling each of said second and third gears with the first-mentioned gear for rotation and reciprocation therewith whereby one of said second and third gears meshes with said gear track during reciprocation of said gears in one direction and the other of said second and third gears meshes with said gear track during reciprocation of said gears in The opposite direction.
 2. Drive mechanism as set forth in claim 1, wherein each of said gears is provided with a shaft rigid therewith and projecting therefrom and said gear coupling means comprises first, second, and third intermeshed spur gears mounted on the respective gear shafts.
 3. Drive mechanism as set forth in claim 2, including a power-driven gear in mesh with one of said second and third spur gears for rotating the same.
 4. Drive mechanism comprising: a reciprocable driven member having a continuous gear track; guide means restraining said member for movement along a rectilinear path of travel; a reciprocable drive gear in mesh with said gear track, said drive gear being rotatable to effect reciprocation of said driven member as the drive gear is reciprocated; a drive shaft for effecting rotation of said drive gear; an elongated linear frame element transversely disposed adjacent said member; a body disposed within said element, said drive shaft being journaled in said body and supported by the latter whereby said frame element guides said body and thus said drive gear along a rectilinear path of reciprocation; means projecting from said member and presenting a pair of spaced surfaces parallel with said path of travel; and first and second spaced guides supported by said body and projecting therefrom whereby as said body reciprocates with said drive gear said guides alternately engage the respective surfaces as said member reciprocates, each of said surfaces comprising a pair of spaced, parallel stretches joined at the ends by interconnecting portions to define a continuous track and each of said guides is disposed for continuous engagement with a corresponding track.
 5. Drive mechanism as set forth in claim 4, wherein said member includes a generally elliptical internally toothed portion presenting said gear track.
 6. Drive mechanism as set forth in claim 4, including a second elongated linear frame element transversely disposed adjacent said member on the side opposite the firstmentioned frame element; a second body supported by said second frame element, said drive shaft being journaled in said second body; means projecting from said member and presenting a second pair of spaced surfaces on the side of said member opposite the first-mentioned surfaces and parallel with said path of travel; and second and third guides supported by said second body and projecting therefrom for continuous engagement with a corresponding track as said second body reciprocates with said drive gear. 